1. Field of the Invention
The present invention relates to a macro lens, and more particularly to an in-focus macro lens, and an imaging apparatus incorporated with the macro lens.
2. Description of the Background Art
A macro lens is a lens capable of close-up photography at a photographing magnification such as the same size. It is an ordinary practice that a macro lens is used for photographing objects in a wide range from an infinite object to a close distance object. In view of the above, it is required to correct aberrations in a satisfactory manner in the wide range for focusing. In recent years, as disclosed in e.g. Japanese Unexamined Patent Publication No. 2011-180226 (patent literature 1), a so-called floating system of moving plural lens groups for focusing is mainly employed. On the other hand, there is also proposed a method in which only one lens group is moved in focusing, as disclosed in Japanese Patent No. 4,874,852 (corresponding to Japanese Unexamined Patent Publication No. 2008-257088, patent literature 2), without employing the floating system for focusing.
Further, in recent years, in the field of cameras (imaging apparatuses), digital cameras have been generally used, in place of silver-halide cameras. Furthermore, moving image photographing can be performed, in addition to still image photographing by auto focusing. In the moving image photographing, in order to keep an in-focus state with respect to movement of an object, control of wobbling a focusing lens group at a high speed for moving the focusing lens group in such a manner as to constantly obtain a maximum value of contrast is performed. Japanese Unexamined Patent Publication No. 2011-048232 (patent literature 3) discloses a macro lens, as an example of macro lenses suitable for such a control.
In the case where a floating system is employed as disclosed in patent literature 1 and in patent literature 3, it is possible to reduce the aberration variation in the range from an infinite distance to a closest distance to a relatively small value. However, in the floating system, it is necessary to move plural lens groups. This may complicate the mechanism, and may increase production error such as backlash or play in a movable lens group. Thus, sufficient stability may not be obtained.
In patent literature 2, a lens group to be moved in focusing is only one among the plural lens groups. Accordingly, the above problem relating to stability may be suppressed. However, in order to obtain stable imaging performance (satisfactory aberration correction) in the range from an infinite distance to a closest distance, it is necessary to sufficiently suppress various aberrations by the lens group to be moved in focusing. This may increase the number of lens elements constituting the lens group to be moved in focusing, and may obstruct high-speed focusing as disclosed in patent literature 3.
Further, in the moving image photographing, it is an ordinary practice to record sounds simultaneously with recording images. In view of the above, it is required to suppress noise such as operating noise generated in a camera or in a macro lens as much as possible. Generally, noise generated in a macro lens is operating noise of an actuator to be used in a focusing operation (wobbling operation). It is necessary to provide a countermeasure against operating noise of an actuator. It is important to reduce the load of an actuator by reducing operating noise of the actuator, as a countermeasure against noise. Thus, in this aspect also, it is required to reduce the weight of a lens group to be moved in focusing.